State of the art technologies for the manufacturing of fatty alcohols from vegetable oils and fats are high or low pressure transesterification with methanol and suitable catalysts followed by high pressure hydrogenation. While high pressure transesterification has the advantage that unrefined oils and waste fat streams with high amount of free fatty acids can be used as raw materials, one major disadvantage is that impurities contained in the crude raw materials, like aldehydes, ketones and phenols are converted in the transesterification and hydrogenation steps into chemical species, which are difficult to separate from the fatty alcohols and reduce the quality of the final products. On the other hand, for low pressure transesterification with e.g. sodium methylate as catalyst the final product qualities are better due to the use of refined oils as feed materials, but higher raw material prices need to be accepted.
According to the state of the art many different processes for processing oils and fats of different qualities are known. For example, EP 0127104 B1 (Cognis) discloses a process for making fatty acid esters of short-chain, aliphatic alcohols by catalytic transesterification of natural fats and/or oils containing free fatty acids (oil phase) with the corresponding alcohols, the oil phase is subjected to preliminary esterification with the alcohols in the presence of acidic esterification catalysts at temperatures no higher than 120° C. and under pressures of less than 5 bar and in the presence of a liquid entraining agent substantially immiscible with the oil phase, after which the reaction product is separated into an entraining agent phase containing the acidic catalyst and water of reaction and the treated oil phase. Subsequently, the oil phase is then subjected to transesterification while the acidic catalyst-containing entraining agent phase is returned, after at least partial drying, to the preliminary esterification stage. By this process, fats and/or oils with acid numbers of up to 60 can be processed in the preliminary esterification stage to give an oil phase having a low acid number.
EP 1092703 B1 (Cognis) teaches the preparation of fatty acid methyl esters having an acid number of less than 0.1 comprises subjecting a fatty acid glyceride, having an acid number of 5 to 20, with methanol in a ratio of 0.4 to 0.7% w/v to a two stage esterification process comprising a first high-pressure and a second low-pressure esterification
Unfortunately, none of the processes according to the state of the art provide a simple and economic method to convert cheap unrefined oils into high quality fatty acids.
One or more embodiments of the invention provide cheap—which means in particular unrefined—fats and oils as raw materials available for producing purified, high quality fatty acids serving as intermediates for fatty acid alkyl esters and—as the following stage of derivatisation—fatty alcohols also showing an improved quality. In particular, it is the essence of the proposed new process to substantially remove unwanted by-products such as ketones, aldehydes and phenols and to collect them in a fraction of waste material, said fraction representing less than 1% b.w. calculated on the total amount of raw material subjected to the purification process. In the context of the present invention the term “to substantially remove” shall have the meaning to remove at least 80, in particular at least 90 and more preferably about 95% of unwanted ketones, aldehydes and phenols from the unrefined oils.